2 Unix

Of the three (Unix, Linux and Windows), Unix was the first. There were numerous operating systems before Unix. However, Unix is special because it gained cross platform popularity, as well as its rich family and extended family of versions.

The history of Unix started with the first release in 1969 for the DEC (Digital Equipment Corporation) PDP-7 machine. It was initially developed by AT&T (American Telephone and Telegraph Company, now known as AT&T Corporation). Back then, the source code of Unix was distributed to government and academic organizations. This led to an explosion of variants in later years.

As the license from AT&T evolved to be more restrictive (mostly intended for commercial uses), researchers at U.C. Berkeley used the base code to develop BSD releases. Both the AT&T and BSD releases of Unix continue to be customized by manufacturers for their specific machines. This gave rise to HP-UX (Hewlett Packard), AIX (IBM), Xenix (Microsoft/SCO), Solaris (Sun Microsystem), Ultrix (DEC) and many other proprietary customization of Unix.

Core to all variants of Unix are some important concepts:

• Portable: a good portion of Unix is written in the C programming language. As such, it is relatively easy to make Unix available to a new processor architecture given that a C compiler is available for it.
• Multi-tasking: Unix can run multiple programs at the same time. While this may seem obvious by today’s standard, it was a break through back when Unix was first written.
• Everything is a file: alright, maybe not everything. However, most resources and status are reflected as files in Unix. This continues to be a characteristic of Unix.
• Pipes: a pipe is a special file that permits two programs to communicate. As one program writes to this special file, another program can read from it to get the data.
• KISS command-line programs: most command-line programs follow the philosophy of keep-it-simple-(and)-stupid. This means that each program can only perform some simple function. However, when combined with the “pipe” concept, programs can string together to perform more complex operations. Unix offers a large number of such KISS commnand line programs.
• File system hierarchy: all Unix systems share the same overall file system hierarchy. This means that specific folders serve specific purposes.
• Plain text configuration: most, if not all, configuration information is stored in plain text files. This makes it easy to alter configurations, as only a text editor is needed.